Genetic diversity determined by agronomic traits and SSR markers in two South American orange‐fleshed sweetpotato breeding populations with potential for population hybrid breeding

Abstract

Orange‐fleshed sweetpotato [Ipomoea batatas (L.) Lam.] (OFSP) breeding populations have gained importance for food security and health reasons. This study's main objectives were to determine genetic diversity in parental material of two OFSP populations developed in Peru (Jewel [PJ] and Zapallo [PZ]) relative to mega‐clones (MCs) using agronomic traits and simple sequence repeat (SSR) markers and to determine whether PJ and PZ are mutually heterotic by developing a PJ × PZ hybrid population (H0). Field trials were performed with clones for PJ (n = 49), PZ (n = 31), MC (n = 21), and H0 (n = 6,898) in Peru. Traits recorded were storage root yield (RYTHA), number of commercial roots per plant, foliage yield, biomass, harvest index, and dry matter (RDM), β‐carotene (RBC), protein, starch, sucrose, iron, zinc, and calcium content of storage roots. Sixty‐six pairs of SSR primers were used to determine molecular diversity. Statistics used were linear mixed models, principal component analysis, and standard procedures for molecular data. New genetic variation was found in PJ and PZ (e.g., RDM ≥29% with RBC ≥25 mg 100 g−1 dry weight basis). For most traits, genetic variance in PJ and PZ was as large as in MC. The SSR marker data clearly separated PJ and PZ into two gene‐pools, together covering nearly the entire MC molecular diversity. Average RYTHA in H0 was high (40.7 t ha−1) with average heterosis increment of 21.8% and range −30.6 to 139.4%. The PJ and PZ lend themselves to study of the efficiency of reciprocal recurrent selection in sweetpotato population hybrid breeding.

Heterosis and Responses to Selection in Orange-Fleshed Sweetpotato (Ipomoea batatas L.) Improved Using Reciprocal Recurrent Selection

“…Early and late harvest plots in H 1 -O-WAE trials were completely randomized as double plots, which are facilitating the harvest at different time points and the statistical analysis as a repeated measurement design, including correlations between early and normal harvests. Analysis within experimental sites revealed a good quality of phenotypic data ( Table 1 ), with means and heritabilities consistent with previous reports [for an overview, see Grüneberg et al (2015) as well as Diaz et al (2021) ].…”

“…The H 1 populations were evaluated at two contrasting sites in Peru: Cañete on the arid Pacific coast, with similarities to a Mediterranean climate; and Satipo in the humid tropics of the Amazon basin. The CIP has made good experience in evaluating breeding material in these contrasting climates for more than a decade [for more details, see Diaz et al (2021) ]. The trials for each hybid population were conducted at each site in separate but adjacent fields during the same season, except for H 1 -O-WAE early and late harvest in Cañete; due to delays in the availability of field area, this trial partially overlapped with the winter season at the Peruvian coast (night and day temperature of about 11 and 19°C, respectively).…”

“…The PJ and PZ pools are clearly distinguishable using pedigree and molecular marker data. Together, they cover nearly the entire diversity of sweetpotato, anchored by 21 mega-clones, and are mutually heterotic ( Diaz et al, 2021 ). To establish the RRS program ( Figure 1 ), 49 PJ and 31 PZ founder clones were selected ( Supplementary Table 1 ).…”

“…To establish the RRS program ( Figure 1 ), 49 PJ and 31 PZ founder clones were selected ( Supplementary Table 1 ). From these clones, a PJ × PZ hybrid population 0 (H 0 ) was developed in Cycle 0 (C 0 ), and H 0 hybrids (see Figure 1 , top left) were evaluated at two sites: (i) Huaral (11°31′S, 77°14′W) on the arid Pacific coast, corresponding to a Mediterranean temperate climate; and (ii) San Ramon (11°07′S, 75°21′W) in the humid tropics of the Amazon basin [for details concerning sites and trials, see Diaz et al (2021) ].…”

“…Kivuva et al (2015) observed a range of mid-parent heterosis for storage root yield from −43 to 92% under no-drought stress and −54 to 82% under drought stress in 15 F 1 hybrids derived from an applied breeding population. Diaz et al (2021) reported mid-parent heterosis for storage root yields ranging from −30.6 to 139.4%, with a mean of 21.8% in 210 F 1 hybrids, tracing back to two parental gene pools. The extent of heterosis is, thus, considerable, and its systematic exploitation deserves a deeper consideration as a novel avenue to increase the productivity and climate resilience.…”